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extern crate proc_macro;
extern crate syn;
#[macro_use]
extern crate quote;
use proc_macro::TokenStream;
use syn::DeriveInput;
#[proc_macro_derive(VariantName)]
pub fn variant_name(input: TokenStream) -> TokenStream {
let input: DeriveInput = syn::parse(input).unwrap();
let name = &input.ident;
let expanded = match input.data {
syn::Data::Struct(_) => {
quote! {
impl VariantName for #name {
fn variant_name(&self) -> &'static str {
stringify!(#name)
}
fn variant_names() -> &'static [&'static str] {
&[stringify!(#name)]
}
}
}
}
syn::Data::Enum(enu) => {
let branches = enu.variants.iter().map(|v| {
let ident = &v.ident;
let match_identifier = match v.fields {
syn::Fields::Named(_) => {
quote! {
#ident{ .. }
}
}
syn::Fields::Unnamed(_) => {
quote! {
#ident( .. )
}
}
syn::Fields::Unit => {
quote! {
#ident
}
}
};
quote! {
&#name::#match_identifier => stringify!(#ident)
}
});
let names = enu.variants.iter().map(|v| v.ident);
quote! {
impl VariantName for #name {
fn variant_name(&self) -> &'static str {
match self {
#(#branches),*
}
}
fn variant_names() -> &'static [&'static str] {
&[#(stringify!(#names)),*]
}
}
}
}
syn::Data::Union(_) => panic!("VariantName can only be derived for Enum or Struct!"),
};
expanded.into()
}